The author presents a new equation that is believed to indicate more accurately the population growth of the coffee berry borer - Hypothenemus hampei (Ferr.) - under ideal environmental conditions. This new equation is based on previously published data by the author (2) and takes into account results of other biological studies (1) concerning this insect. It is now possible to calculate the percentage of attacked coffee fruits at any given time "t", between the limits 0 and 4, by the formula Pt0(4)- 100 / 1 + (20.02/iq - 1) e - 2.303 [log (20.02 - iq) / (1 - iq)] t where i = initial infestation factor q = average number of active females, per coffee fruit, in the moment when "i" is determined. The derived equation is chiefly based on the following biological data : a) the normal sex ratio is 1 male to 9.75 females ; b) only the females attack the fruits; c) an active female may, during the season of fruit development, attack as many as four fruits in the field, and in each fruit can deposit an average of 20.97 eggs. In this paper three theoretical examples are given of the application of the new equation, and the results obtained show the importance of the initial infestation factor in the final percentage of attacked coffee fruits.